'grown' ultimately comes from Old English, specifically the verb 'grōwan', where the root 'grō-' meant 'to grow, to become green or increase'.

'grōwan' in Old English developed into Middle English forms like 'growen' and then into Modern English 'grow'; the past participle forms (earlier 'growen') evolved into the modern 'grown'.

Initially it meant 'to become larger or to spring up', and over time it broadened to include 'mature, increase, develop' in modern usage.